| 摘要 |
PURPOSE:To provide the title device to detect the focus position with good accuracy even in case of the light beam of high energy detecting the focus position of the light beam with the detection of the ultrasonic wave propagating the inside of a projecting piece by generating at the time when the light beam is projected on the light beam projecting piece. CONSTITUTION:In this invention the projecting part is deflected by the thermal expansion by the light beam 12 projecting on the light beam projecting piece 1 and an ultrasonic wave is caused from this part. When the focus F of the light beam 12 is not coincided with the surface of the projecting piece 1, the plane wavy propagation component of the ultrasonic wave propagating into the projecting piece 1 becomes more. On the other hand, in case of the focus F of the light beam 12 being coincided with the surface of the projecting piece 1, the spherical propagation component becomes more. Ultrasonic wave detectors 1a-1e detect such propagation waves, which are given to a focus position calculating means. Said means then calculates the position equivalent to the the detection result of the position detector 8 of the time of discriminating of locating on the focus F of the light beam 12 of the projecting piece 1 as the focus position of the light beam 12 from the detection result of the detectors 1a-1e. |
